Labels on lawn care products list the rate at which the product should be applied. Some labels will also list the correct setting for some name-brand spreaders. However, these settings are just recommendations to provide a good reference point when calibrating spreaders (Fig. 12). Seldom does a setting give the same application rate in all operating conditions and application sites. Variables such as particle size, particle density, particle shape, relative humidity of the granule, ambient relative humidity, drop point of granules on the impeller plate, impeller speed and ground speed all affect the application rate and the distribution pattern. Therefore, granular applicators should be calibrated for each type of granular product being applied and for change in operator, weather and field conditions.
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| Fig. 12. Spreader settings listed on product labels provide a good starting point when calibrating. |
Before beginning to calibrate a granular applicator, be sure that it is clean and all parts are working properly. Always wear rubber gloves and other protective clothing to prevent contact with chemicals during cleaning and calibration of equipment and actual application of chemicals.
The primary purpose of calibration is to determine the actual delivery rate of a spreader regardless of its type. However, with rotary spreaders, it is also necessary to check and correct the distribution pattern.